Are you RingOfSet?
There is no issue with guards at all in those instances, unless those guards don't know what they are doing/the rest of the group is awful. S&S Guard gives good dps buffs to the group with a good duration and a short cooldown so the slight loss of dps is really negligible. Btw brute conqs don't do more dps than s&s guards, even in pvp. In fact I am often outdpsing brute conqs Pole guard actually weakens the group more than s&s guard (because in def stance it's a tiny dps difference with s&s while not bringing any group buffs) unless he gets the chance to go frenzy a lot.
I have only done 2 of those two instances (caravan and halls) and I honestly find them a little dull and somewhat easy (but I don't mind the latter and my group was a bit too OP to judge that properly I guess). Some boss fights are ok but I have mixed feelings about the whole thing and I know I won't be farming those instances (same feeling with Coils).